This invention relates generally to a method and apparatus for remotely determining the optical clarity or transmissivity of water and other mediums; and for remotely determining depth of water and other mediums. More particularly, this invention relates to a novel system for determining the diffuse attenuation coefficient or K factor for large areas of water and other mediums from a remote location and over a short period of time; and for remotely determining depth in water and other mediums over large areas and short periods of time.
The clarity or transmissivity of water is, in part, dependent on a factor known as K which is the diffuse attenuation coefficient. Thus, the determination of the K factor for a body of water will, in turn, provide information on water clarity. It will be appreciated that knowledge of water clarity (and K factor) is quite important for a variety of scientific, environmental and military applications. For example, information on sea water clarity is important to both Oceanographers and naval forces. Oceanographers are interested in determining the optical transmissivity of sea water because this information is useful in determining the density of phytoplankton (organisms) and its effect on the entire food chain; and in determining the sunlight available to sea organisms for photosynthesis.
Similarly, naval forces are interested in mapping water clarity for several reasons. First, absorption of visible light seriously hampers laser communications systems which may operate between a submarine and another submarine, a surface ship, an airplane, or a satellite. Therefore the effectiveness of such a secure communications link depends critically on knowing the sea water optical properties around the globe. Second, the effectiveness of some nonacoustic antisubmarine warfare (ASW) detection systems depends critically on the water optical transmission properties. Therefore it is essential to have water clarity data to judge the utility of such ASW systems. This is important at shallow depths and also to determine the depth of the thermocline.
The K factor is also important in pollution monitoring. Pollutants dissolved in water or floating on the surface must be detected accurately and over a short time period. Moreover, if the discharge is still in progress, detection of K factor can be used to trace the pollution back to the primary source.
K factor can also be utilized in bathymetry for detecting the bottom of a relatively shallow lake, river or ocean. This is of interest to hydrologists who want to know, for example, the flow rates of rivers (where water depth is needed). Cartographers are also quite interested in mapping ocean depths near shorelines and harbors to provide safe navigational passages.
Unfortunately, there is presently no known method which determines K factor readings as well as water depths from a remote location (e.g. airborne) over wide areas with sufficient accuracy in very short time periods and in a very cost effective manner. Prior art methods for ascertaining K factor typically utilize wire line devices which are cumbersome and time consuming. Such wire line devices also are limited to ascertaining K in limited areas as opposed to large areas.